As optical signal and opto-electronic communications have come into prominence in recent years, numerous optical couplers have been devised to couple one fiber-optic cable to another. Generally these couplers have been directed to coupling two stationary cables together. However, more recently, the need to couple moving fiber-optic cables together has come into being. In response to this need, devices such as the Fiber Optic Rotating Joint (FORJ) have been developed. In a FORJ coupler, an optical fiber such as that used in communications, is coupled through a rotating joint to another optical fiber. In this manner, one of the optical fibers can move or pivot while the other remains stationary. One illustrative use of such a FORJ coupler is on military tanks wherein a FORJ coupler is mounted on the base of the rotating turret to maintain communications with the body of the tank. An example of one FORJ coupler is the "Off-Axis FORJ" which is available from Litton Poly-Scientific.
One problem encountered in FORJ coupler design is significant signal loss as the signal is transmitted through the FORJ device. Another problem encountered in FORJ devices is undesired wear and friction within the device as portions of the device rotate. Moreover FORJ couplers such as the one referenced above require digital data and need active electronics at the input and output of the coupler. Insertion loss of this FORJ coupler can be quite high, for example approximately 20 dB. The amplitude of the output signal can also vary significantly when this FORJ coupler is rotated.